[Proposal] Selector expressions

Suppose we have an array named arr, and want to select items > 3:
```VB.NET
dim result = arr.Select(function(x) x > 3)
```

I want to rewrite it like this:
```VB.NET
dim result = arr[#Item > 3]
```

Note:
In #556, I asked for allowing [] for arrays and indexer. I am using this here to avoid any confusion with any old code using `()`.

It items are objects with properties:
```VB.NET
dim result = Students.Select(function(x) x.Name)
```

then:
```VB.NET
dim result = Students[#Item.Name]
```

Which can be shorten to:
```VB.NET
dim result = Students[#Name]
```

note that I previously wanted to use dot instead of #, but this can cause some confusion inside With Blocks.

Now, Suppose we have a list like this:
```VB.NET
Dim Students as List(Of Student)
```

lets complicate the selector a little:
```VB.NET
dim result = Students.Select(function(x) x.Address.Street(0) = "a" OrElse x.Address.Street(0) = "a")
```

or with LinQ:
```VB.NET
dim result = from x in Students
Let startsWith = x.Address.Street(0)
Where startsWith = "a" OrElse startsWith = "a"
Select x
```

We can make this shorter by defining a var for the selector and reuse it:
```VB.NET
dim startsWith = #Student.Address.Street(0)
dim result = Students[startsWith = "a" orelse startsWith = "b" ]
```

Note using the type #Student so we avoid late binding and have intellisense support.
which can be more compact if VB always the in array syntax:
```VB.NET
dim result = Students[startsWith in {"a", "b"}]
```

or in another way (since the selector is an expression tree, if can be some sort of a function delegate expression:
```VB.NET
dim startsWith = #Student.Address.Street.StartsWith
dim result = Students[startsWith("a") orelse startsWith("b") ]
```

and if add a StartsWithAny extension method to the string class:
```VB.NET
dim startsWith = #Student.Address.Street.StartsWithAny
dim result = Students[startsWith({"a", "b"}) ]
```